Method of shaping filaments



May 14, 1929. w. GERQ METHOD OF SHAPING FILAMENTS Filed Sept. 24, 1925 F'IG.|

- lNVENTOR WILLIAM B. GERO BY ATTORNEY Patented May 14, 1929.

UNITED STATES PATENT OFFICE.

WILLIAM BENJAMIN GERO, OF BLOOMFIELD, NEW JERSEY, ASSIGNOB TO WESTING- HOUSE LAMP COMPANY, A CORPORATION 01' PENNSYLVAHIL METHOD OF SHAPING FILAHENTS.

Application filed September This invention relates to the shaping or forming of filaments and more particularly to a method of shaping drawn tungsten filaments produced according to the process de- 5 scribed in Coolidge Patent No. 1,082,933 issued December 30, 1913, for use as cathodes for electron discharge devices, incandescent lamp illuminants, etc.

In the manufacture of electron discharge devices employing concentrically arranged electrodes, it is desirable that the filamentary cathode be closely and accurately spaced with respect to the electrodes but it is essential that it does not come in contact therewith and short circuit the same.

Tungsten wire produced according to the Coolidge process is extremely curly and cannot be mounted without preliminary shaping. Moreover, due to the necessity of using a carbonaceous lubricant in the wire drawing operation, the wire becomes coated with a closely adherent layer of carbon.

Heretofore, in the manufacture of radio tubes, employing .thoriated cathodes, it has been the usual practice, in order to prevent the filamentary cathode from coming into contact with the grid through distortion or irregularity in the shape of the filament and to facilitate mounting thereof, to shape the filaments after activation and while they are still curly by winding them .on a special metal form and heating to a high temperature in hydrogen or other inert environment. This treatment eliminates the tendency of the filaments to curl and causes them to conform to the shape of the metal form on which they are wound.

Difiiculty has been experienced, however, in. forming filaments by this process since the high heating required to cause the filaments to take the desired shape renders them brittle and consequently results in a large proportion of broken filaments. A large loss of filaments also occurs during shaping, due to the difference in the rate of expansion of the tungsten wireand the metal form on which it is wound. a

Furthermore, it is frequently desirable to activate the filament prior to forming or shaping thereof since if the activation is erformed after forming, each individual lament length must be activated separately. Activation prior to forming the filaments may consist in flashing the filaments in a hy- 24, 1925. Serial No. 58,280.

drocarbon vapor by the continuous process set forth in application Serial No. 578,470 of Italph E. Myers, filed July 29, 1922, and en tltled Actlvation of thoriated filaments, and assigned to the Westinghouse Lamp C0mpany, or a simple flashing in hydrogen may be used, depending on the circumstances and conditions imder which the filaments are to be used. After the filament has been ac tivated, however, it is desirable, in order to maintain the electron emission thereof high, that it be not again heated until after it has been mounted in the discharge device.

One of the objects of this invention, therefore, is to provide an improved method of shaping filaments for mounting in electron discharge devices, etc., which does not necessitate the heating of the filament between the activation thereof and the incorporation of the same into the device.

Another object is to provide an improved method and apparatus for shaping filaments to the exact form which they will have when mounted and to produce shaped filaments of rugged nature.

Another object is to provide an improved method of shaping filaments in which the loss of filaments, due to breakage, will be reduced to a minimum.

Another object is to provide a shaped and activated filament for electron emission devices which is not subjected to high heating after activation thereof and prior to mounting in the device.

Other objects and advantages will hereinafter appear.

In accordance with this invention the drawn tungsten filament is first cleaned and straightened by heating at a red heat in air and subsequently to a white'heat in hydrogen, the wire being maintained under a slight tension during this heat treatment. The heat treatment in addition to removing the carbon and other impurities from the wire, overcomes desired to. precondition the filament for electron emission purposes, the heatlng 111 hydrogen during the straightening and cleaning.

process may be relied upon to accomplish this purpose.

After the wire has been cleaned, stralghtcued and activated, it is wound, in a cold condition. on a special form under tension. S1nce the wire is both straight and pliable 1t assumes the shape of the form without heat and after being removed therefrom, the lilamcnts retain their shape without any tendency to curl. Mounting of the filament 1n the envelope of the electron discharge device is thereby facilitated. It is only necessary to cut the filaments from the form on which they are wound, into individual lengths. and mount imthe usual manner.

It will be noted that by straightening the wire prior to forming or shaping of the fila ment, that it is not necessary to heat it on the form. In the case of wire not previously straightened or cleaned, however, if heating on the form is not resorted to, the filaments, when removed therefrom, curl and distort, since the part which should be straight has not been relieved of its tendency to curl.

In order that this invention may be more fully understood, reference may be had to the accompanying drawin in wh1ch:

Fig. 1 illustrates iagrannnatically, apparatus for cleaning and straightening the wire Fig. 2 is a diagrammatic showing of the apparatus for winding a wire on a form;

Fig. 3 is an elevation of the guide and 1ts operating mechanism for distributing the wire evenly over the form;

Fig. 4 is a perspective view of the form with the wire wound thereon;

Fig. 5 is an elevation of a shaped filament after removal from the form; and,

Fig. 6 is an elevation of a radio tube partly in section showing the manner of mounting the filament therein.

The black or uncleaned wire 1 as it comes from the final drawing operation is wound on a reel 2 which may be mounted on a suitable standard 3 forming a. part of the apparatus shown in Fig. 1 for cleaning and straightening the wire. The wire is led from the reel 2 and rewound on a second reel 4 mounted on a standard 5 and provided with a suitable winding mechanism sueh as the pulley 6 and belt 7. The reel 2 is provided with any suitable braking mechanism such as a friction disc 8 to subject the wire to a slight tension as it is drawn therefrom by the winding reel 4.

The wire on its way to the reel 4 passes through a. tube or trough 9 open to the atmosphere and supported on standards 10. A mercury cup 11 at the entrance of the tube 9 makes electrical connection with the wire from a. suitable source of current 12 through conductor 13. A second mercury contact ll carried by the hydrogen chamber 15 completes the circuit through the wire 1 and permits it to be heated to a dull red heat during its passage through the tube 9. This heating in air or in an oxidizing atmosphere exerts a boneficial effect upon the filament rendering it soft and more pliable. The wire is then drawn through the chamber 15 to which a stream of hydrogen is supplied by the inlet pipe 16. A mercury contact 17 is secured to the end wall 18 of the chamber amt together with the contact 14;, permits electrical current to be supplied to the wire from the source 12 during its passage through the chamber 15 to heat the. same to ahigh temperature, i. e., about 2000 C. The electric current supplied by the source of power 12 may be controlled by the resistance units 19 and 20.

The high heating of the wire while it is subjected to tension in the hydrogen atmos phere serves to remove the tendency of the wire to curl and leave it straight and clean.

The wire after being cleaned and straightened may be activated in any suitable man, nor to render it capable of high electron emission and may then be wound upon a metal form 21. In the apparatus shown in Fig. 2 for winding the wire 011 the form, the reel 22 containing the wire is mounted on a standard 23 and is provided with suitable braking mechanism, such as the friction disc 24, to subject the wire to a slight tension as it is drawn from the reel.

The form which may be in the shape shown in Fig. 4 is mounted on a standard 25 and rotated in a suitable manner, as by the belt 26 and pulle 27. A guide 28 pivoted at 29 is actuated y the cam 30 driven through the shaft 31 and spiral gears 32 and 33 from the rotating mechanism of the form 21 direct the wire longitudinally of the form as it is wound and thereby serve to maintain the turns separated. A spring 34 returns the guide to initial position after the winding has been completed. The wire is wound on the form without heating and due to the treatment it has received in the cleaning and straightening process, it readily assumes the shape of the form and maintains such shape. It is merely necessary then to remove the wire from the form by cutting alon the grooves 35 on both sides of the form. he filaments, after they have been cut from the form, are in the shape shown in Fig. 5 and readily maintain that shape so that they can be mounted in the radio tube or other device with facility and the likelihood of their short-circuiting or coming into contact with the other electrodes is greatly reduced.

Fig. 6 shows the method of mounting the filament in a three-element radio tube. The tube shown comprises an envelope 36 containmg a plate or anode 37 in the form of a flattened cylinder, an enclosed grid 38 of similar shape, and the filament 39 disposed between the opposed faces of the grid and closely spaced therefrom.

It will be noted that the filament has been shaped between the activation thereof and its incorporation in the device and that the shaping has not necessitated the heating of the wire after activation. Consequently, the electron-emitting property of the wire has not been impaired by the forming operation. Moreover, since the filaments have not been heated on the form, the large loss of filaments which occurs through uneven expansion of the form and filament has been eliminated and there is less probability of embrittlement ot' the wire. The filaments shaped by the above process are extremely rugged and well shaped.

It is to be understood, of course, that many changes may be made in the embodiment illustrated and described without departing from this invention.

What is claimed is:

1. The method of shaping tungsten filaments which comprises straightening the wire at a high temperature under tension and subsequently winding the wire under tension on a form without heat.

2. The method of shaping tungsten filaments which comprises straightening the wire at a White heat under tension and subsequently winding the wire under tension on a form without the application of heat.

3. The method of shaping tungsten filaments which comprises cleaning and straightening the wire in hydrogen at a high temperature and winding the Wire under tension on a form without heat.

4. The method of shaping tungsten filaments which comprises straightening the filament under tension at a white heat in hydrogen, winding the filament under tension on a form Without heat and severing the shaped filament from the form into individual lengths.

5. The method of shaping tungsten filaments which comprises subjecting the filament to tensional strains at a white heat and subsequently forming it under tension into the desired shape for mounting Without the. application of heat.

6. The method of shaping metallic filaments which comprises subjecting the filament to tensional strains at a high temperature in a reducing atmosphere and subsequently forming it under tension without heat into the desired shape for mounting.

7. The method of treating a thoriated tungsten filament preparatory to mounting in an electron discharge device which comprises straightening the filament and rendering it pliable, activating the filament and shaping it withoutheat under tension.

8. The method of treating a thoriated tungsten filament preparatory to mounting in an electron discharge device which comprises subjecting the filament to tensional strains at a high temperature, activating the filament and subsequently forming it while cold into the desired shape.

9. The method of treating a thoriated tungsten filament preparatory to mounting in an electron discharge device which comprises rendering the filament liable and strai ht, activating it and forming into the desired shape under tension without heat.

In testimony whereof, I have hereunto subscribed my name this twenty-third day of September, 1925.

WILLIAM BENJAMIN GERO. 

